Capacitive sensing detection circuit

It is a capacitive sensing detection circuit made of integrated circuits . The circuit mainly consists of a 4-12-input NAND gate integrated circuit
CD4093 (see Figure 6-57b for the internal circuit). R． ,C. and a NAND gate (①, ②, ③ feet, IC 1) of CD4093 to form a 400Hz
square wave oscillator. The square wave output by the oscillator is divided into two channels: one channel is directly sent to a NAND gate circuit (④, ⑤, ⑥ pin, IC2); the other channel
sends an input end of a NAND gate (⑧, ⑨, @ pin, IC3) through the capacitor Cz. Since IC2 is connected in the form of a NOT gate, the potential difference between its input
and output terminals is 180°. , the signal output by IC2 is coupled to the other input terminal of 1C3 through cJ and C4.
    Nanyu IC3's two input terminals have the same level. The phase is opposite, so as long as IC1 oscillates normally. At least one of the two input terminals of 1C3 is
low level, so the output terminal of 1C3 is a stable high level. Due to the effect of G. , rri cutoff. However, if the input signal at any input terminal of IC3 is canceled
or the amplitude of the signal drops below the input threshold level of the gate circuit, 1C3 will output a square wave signal.
    When a conductor approaches the sensing electrode, part of the signal coupled from C¨ to pin ⑨ of the input terminal of IC3 will be shunted to the ground. If
the amplitude of the shunted signal is lower than the threshold level of the NAND gate input terminal, IC 3 A square wave signal will be output. After the signal is rectified by VD1 and VD2,
the switch tube vri will be turned on, and the power of the relay will be turned on to make it close.
    The capacitance c is sufficient to adjust the sensitivity. If you need the circuit to work with maximum sensitivity, you can first adjust G to make the relay just absorb the resistance,
then adjust C4 to make the relay just disconnect, and then seal G tightly with high-frequency wax or insulating paint. Can.
    The components used in the circuit in Figure 6-57 are all ordinary components. Since CD4093 is a CM()S integrated circuit, silver is easily broken down by
the static electricity Therefore, when making it, it is best to solder an integrated circuit socket first. ． - Wait until the circuit is checked and then insert the CD4093 into the socket. The sensing
electrode piece can be cut from a metal can.